FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT
Department of Building, Energy and Environmental Engineering
Building energy pre-design
based on multi-criteria decision analysis
Elisavet Sandalidi
2017
A thesis submitted as a pre-requisite for the Degree of Master of Science in Energy Systems
Supervisor: Arman Ameen Examiner: Taghi Karimipanah
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Abstract
The successful energy design of buildings requires that special attention be paid to the conceptual stage. However, it is a difficult task to find the most promising design
alternatives satisfying several conflicting criteria. This thesis presents a simple multi-criteria decisions analysis method that could assist designers in green building design. Variables in the model include those alternatives that are common options when a residential building is to be constructed. The individual components that are considered are the building envelope, heating, ventilation and air conditioning (HVAC) system, service water heating, power and lighting. The key actors, objectives and methodology of multi-criteria decisions analysis are presented and finally a case study for a residential building in Athens is performed. The criteria by which to evaluate each building component of the newly built construction were identified by the decision-makers. Subsequently, decision frameworks for the selection of roof, walls, windows, heating system, energy source for heating system, power source, lighting and service water heating system were built. The method is followed step-by-step to conclude on the optimal building components based on their score. Due to the equal scoring of the windows and an inapplicable combination of electric underfloor heating with air-to- water heat pump, the method is characterized by low accuracy. The fact that the building components have been treated individually sets the method as a basic one and indicates that a more complex one should be preferred when more trustworthy results are needed.
Keywords: decision-making, building components, multi-criteria decision analysis, residential building, energy pre-design, interests, stakeholders
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1 Contents
Abstract ... iii
Introduction ... 1
1.1 Background ... 1
1.2 Literature review ... 1
1.3 Aims ... 1
1.4 Approach ... 2
2 Energy building pre-design options review ... 3
2.1 Building envelope ... 3
2.1.1 Flat roof, conventional, not-ventilated, trafficable ... 3
2.1.2 Flat roof ventilated, trafficable ... 3
2.1.3 Flat roof with insulation, conventional, non-trafficable ... 3
2.1.4 Aluminium windows with thermal bridge breaking system ... 4
2.1.5 PVC windows with thermal bridge breakage ... 4
2.1.6 Wood windows ... 4
2.1.7 Brick cavity walls, with outer wall of facing bricks, 5 cm thick insulation ... 4
2.1.8 Brick cavity walls with coated outer wall of brickwork, 5 cm thick insulation .. 5
2.1.9 Brick cavity walls with coated outer wall of brickwork, 10 cm thick insulation 5 2.1.10 Back ventilated façade of brickwork, 5 cm thick insulation ... 5
2.1.11 Curtain wall ... 5
2.2 HVAC systems ... 6
2.2.1 Heating system ... 6
2.2.2 Energy source for heating system ... 6
2.3 Power ... 7
2.3.1 Grid fed ... 7
2.3.2 Solar electric or PV system ... 7
2.4 Lighting ... 8
2.4.1 Automatic lighting shutoff ... 8
2.4.2 Space control ... 8
2.5 Service water heating ... 8
2.5.1 Electric water heater ... 8
2.5.2 Thermosyphon system ... 8
2.5.3 Forced circulation system ... 8
2.5.4 Combi system ... 8
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3 Multi-criteria decision analysis ... 9
3.1 The complexity of decisions ... 9
3.1.1 The characteristics of the decision-maker ... 9
3.1.2 The role of the analyst ... 10
3.1.3 The client ... 10
3.1.4 Third parties ... 10
3.2 Objectives of multi-criteria decision analysis ... 11
4 Basic concepts and methodology ... 12
4.1 Multi-criteria decision analysis (MCDA) problem formulation ... 12
5 Process and results ... 13
5.1 Case study ... 13
5.1.1 Step 1: Definition of the decision opportunity ... 13
5.1.2 Step 2: Identify Stakeholder preferences ... 13
5.1.3 Step 3: Build the decision frameworks ... 14
5.1.4 Step 4: Rate the alternatives ... 20
5.1.5 Step 5: Weight Stakeholder interests ... 20
5.1.6 Step 6: Score the alternatives ... 21
6 Discussion ... 25
7 Conclusions ... 25
8 Bibliography ... 26
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Introduction 1.1 Background
The large impact of buildings on the global climate change has made energy efficient design mandatory in many countries around the globe. An energy efficient building is designed with strategies that conserve resources, reduce waste, minimize the life cycle and create healthy environment for people to live and work.
The successful design requires that special attention be paid to the conceptual stage when many potential design alternatives are generated and roughly evaluated in order to obtain the most promising solution. Decisions made in the conceptual stage have considerable impacts on the building performance. Usually, designers rely heavily on previous experience or building energy simulation programs to determine appropriate values for design
parameters. However, the previous experience might lead to incorrect conclusions because they cannot cover every foreseeable circumstance and cannot reflect the complicated interactions between various parameters. Although many sophisticated energy simulation programs are valuable to study the impacts of design parameters on building performance, the iterative trial-and-error process of searching for a better design solution is difficult to manage. Moreover, the process of feeding the energy design software with all the possible combinations could be particularly time-consuming and ineffective. (Wang, Zmeureanu, &
Rivard, 2005)
1.2 Literature review
Methods for decision-making in the early design stage of buildings have become increasingly popular in recent years. Extensive literature for these methods is available in web databases of scientific research. Wang et al. (2009) conducts a review of methods for the analysis and the criteria weighting while Pacheco et al. (2012) present an extensive list of criteria.Wang et al. (2005) employ a life cycle analysis methodology to evaluate design alternatives within an economical and environmental perspective. In this study, little attention is given to the building owner’s preference system. Moreover, it focuses on building envelope only. For the building envelope, a multi-objective search was also performed through genetic algorithms aiming to minimize the energy need for heating, cooling and lighting of a case study (Echenagucia, Capozzoli, Cascone, & Sassone, 2015). Results highlighted a smal overall window-to-wall ratio. Huedo et al. (2016) propose an innovative model for the sustainable selection of building envelope assemblies. However, the evaluation model is rather complicated and does not offer a quick evaluation process.
1.3 Aims
The aim of the thesis is to explore the available design options offered for each building component in order to facilitate the energy engineer during the process of setting the technical characteristics for a newly built or retrofitted building. Α multi-criteria decision analysis will be conducted for deciding on the optimal technical characteristics. This pre- selection can be considered a step before proceeding with the energy design process.
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1.4 Approach
This thesis presents the use of a multi-criteria decision method which allows the exploration of an optimal solution for the predefined problem of building energy pre-design. The various design options offered for each building component in order to achieve energy efficiency will be demonstrated. Due to the fact that the purpose of the thesis is to facilitate the designer, the list of design options will not be exhaustive. Instead, the most commonly design options in Greek buildings will be identified. Moreover, alternative criteria that could be taken into account during the design process will be proposed and discussed. Subsequently, the
methodological process of multi-criteria decision analysis will be described and the optimum method will be chosen. A case study of a new building will be set as implementation
example where the design options available on-site will be analyzed based on the method selected.
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2 Energy building pre-design options review
For the energy efficient building design, the technical requirements for the distinct components of the building must be defined. The ASHRAE/ANSI/IES standard 90.1 -2010 Energy Standard for Buildings Except Low-Rise Residential Buildings divides the building entity in five sections representing the technical distinct components of the building. This organization of sections is adopted in this thesis. The individual components are the building envelope, heating, ventilation and air conditioning (HVAC) system, service water heating, power and lighting. Various energy efficient options are available for the design of each component. These options create multiple combinations of design scenarios.
2.1 Building envelope
Below, most commonly used building envelope assemblies are identified. (Huedo, Mulet, &
Lopez-Mesa, 2016)
2.1.1 Flat roof, conventional, not- ventilated, trafficable It consists of finishing ceramic tiles (P), mortar (MA), two layers of polypropylene geotextile (Csa), waterproof bitumen sheet (I), thermal insulation (AT), vapour barrier (B), aerated concrete for roof slope (FP), reinforce concrete one-way slab with ceramic hollow plot (SR) and plastering (RI).
2.1.2 Flat roof ventilated, trafficable It consists of finishing ceramic tiles (P), mortar (MA), two layers of polypropylene textile (Csa), double waterproof sheet bitumen (I), ceramic tiles for roof slope (FP), ventilated air chamber (C), thermal
insulation of mineral wool (AT),
unidirectional fabric forging with ceramic elements and plastering (RI).
2.1.3 Flat roof with insulation, conventional, non-trafficable It consists of finishing gravel (P), two layers of polypropylene textile (Csa), thermal insulation (AT), double waterproof sheet bitumen (I), aerated concrete for roof slope (FP), reinforced concrete one-way slab with ceramic hollow plot (SR) and plastering (I).
4 2.1.4 Aluminium windows with
thermal bridge breaking system It consists of double glazing, aluminium frame with thermal bridge breaking system, filler of neutral silicon, dry air space,
ironwork of steel and galvanized steel subframe.
2.1.5 PVC windows with thermal bridge breakage
It consists of double glazing, PVC frame with three chambers, filler of neutral silicon, dry air space, ironwork of steel and galvanized steel subframe.
2.1.6 Wood windows
It consists of double glazing, high density wood frame, filler of neutral silicon, dry air space, ironwork of steel and wood frame.
2.1.7 Brick cavity walls, with outer wall of facing bricks, 5 cm thick insulation
It consists of exterior masonry wall of ceramic perforated brick with cement (LC), intermediate coat (a plaster on the interior face of the principal with cement mortar) (RM), non-ventilated air chamber (C), thermal insulation (mineral wool) (AT), inner skin of double hollow ceramic brick with cement mortar joints (LH) and plastering (RI).
5 2.1.8 Brick cavity walls with coated
outer wall of brickwork, 5 cm thick insulation
It consists of continuous outer coating with cement mortar (RE), exterior masonry wall of perforated ceramic brick with cement mortar joints (LC), non-ventilated air chamber (C), thermal insulation (mineral wool) (AT), inner layer of double hollow ceramic brick with cement mortar joints (LH) and plastering (RI).
2.1.9 Brick cavity walls with coated outer wall of brickwork, 10 cm thick insulation
It consists of continuous outer coating with cement mortar (RE), ceramic brick with cement mortar joints (LC), non-ventilated air chamber (C), thermal insulation (mineral wool) (AT), inner layer of double hollow ceramic brick with cement mortar joints (LH) and plastering (RI).
2.1.10 Back ventilated façade of
brickwork, 5 cm thick insulation It consists of outer discontinuous coating of ceramic tiles mechanically fastened with aluminium substructure type T (RE), ventilated air chamber (C), thermal
insulation of mineral wool (AT), continuous outer coating with cement mortar (RM), inner layer of double hollow ceramic brick with cement mortar joints (LC) and plastering (RI).
2.1.11 Curtain wall
It consists of double glazing, aluminium substructure of tubular mullions and horizontal transoms, dry air space and aluminium composite panel.
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2.2 HVAC systems
2.2.1 Heating system 2.2.1.1 Radiator heating
Central heating with radiators has been the dominant way of heating residential buildings since the mid-20th century. Hot water circulates through a system of pipes inside a house to warm radiators. Radiators are usually placed under windows or next to doors in order to provide maximum efficiency.
2.2.1.2 Underfloor/wall/ roof heating
In underfloor heating system, the basic equipment used is identical to the one used for radiator heating. The main difference is that the heat emitter is the floor, or wall/roof in wall/roof heating instead of the radiators. The floor must be thermally insulated underneath to eliminate heat losses and pipes are laid on it.
2.2.1.3 Electric underfloor heating
The basic principle of electric underfloor heating is the same to the hot water underfloor heating. The difference lies in the fact that a series of electric wires are installed instead of pipes.
2.2.1.4 Fireplace insert
A fireplace insert is a fireproof box surrounded by steel or cast iron and fronted by insulated glass, creating a closed combustion system. It is like a wood stove modified to fit within the firebox of a masonry fireplace. Through vents under the firebox, room air is drawn in, heated through a heat exchanger and sent back into the house either through vents at the top of the fireplace or through ducts leading to nearby rooms.
2.2.1.5 Passive heating
In recent years, a growing interest for passive heating and cooling has been arising. Passive systems are based on the natural convective air movement using natural heating and cooling sources. However, they do not exclude electrical energy use to a small extent.
In passive heating, certain building elements are used to store heat. The most common application is the Trombe wall, a wall which interposes between the inside and a wall glazing. Between the Trombe wall and the wall glazing, there is air cavity which acts as the heat convection medium. Two air vents at the top and bottom of the wall allow the circulation of heat from the outside into the room. (Pacheco, Ordonez, & Martinez, 2012) 2.2.2 Energy source for heating system
2.2.2.1 Oil
Oil-fired boilers are high temperature systems usually combined with hydronic radiators.
Due to the current developments in the international oil prices, oil use has significantly been reduced. Its high values of carbon dioxide emissions (68,479980 g/MJ) and sulphur dioxide emissions (0,4821240 g/MJ) have led to energy policies which complementary contribute in the reduction. (Papadopoulos, Oxizidis, & Papandritsas, 2008)
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The introduction of natural gas has broadened the options for central heating in the major cities. (Papadopoulos, Oxizidis, & Papandritsas, 2008). In newly built or retrofitted buildings, natural gas is generally the preferred energy source thanks to lower cost and limited carbon dioxide emissions (50,234390 g/MJ) and sulphur dioxide emissions (0,0002512 g/MJ).
2.2.2.3 Wood and pellet
Pellets are classified as a form of renewable energy. They are made from compressed organic matter or wood. Fireplace inserts can be fueled either with wood or pellets.
2.2.2.4 Electrical energy
Many homeowners consider electrical energy as an option for heating their premises.
Electricity can be used as the sole heating source or in combination with other sources in a home heating system. The five basic types of electric heating systems available are as follows:
forced-air systems (e.g. electric resistance heating)
hydronic or hot water systems (usually electric floor heating)
room heaters
radiant systems
combination systems with plenum heaters in the hot air plenum.
2.2.2.5 Renewable energy combined with electrical energy (heat pump)
Heat pumps are forced air systems using electricity to transfer heat from either ambient air (air/water heat pumps) or ground (geothermal heat pumps). Air/water heat pumps work in a similar way to the refrigerators using a steam compression cycle. The pump consists of the following main parts: a compressor, a relief valve and two heat exchangers (an evaporator and a condenser).
The outside air is forced through a fan to the heat pump where it meets the evaporator. The latter is connected to a closed system containing a coolant that can be converted to gas at very low temperatures. When the outside air hits the evaporator the coolant is converted into gas.
Then, using a compressor, the gas reaches a fairly high temperature to which it can be transferred to the condenser of the home heating system. At the same time, the coolant returns to the liquid form with the help of the condenser, ready to be converted into gas once again and to collect new heat.
2.3 Power
2.3.1 Grid fed
This is the conventional way of powering a home where homeowners are fully dependent on the utility retail prices.
2.3.2 Solar electric or PV system
A grid-connected home solar electric or PV system receives back-up power from a utility's grid when the PV system is not producing enough power. When the system produces excess
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power, the utility is required to purchase the power through a metering and rate arrangement.
Net metering is the best arrangement. Under this arrangement, the power provider essentially pays the retail price for the electricity fed back into the grid.
2.4 Lighting
2.4.1 Automatic lighting shutoff
Interior lighting in buildings can be controlled with an automatic control device to shut off building lighting in all spaces. This automatic control device can function on either
a. A scheduled basis using a time-of-day operated control device that turns lighting off at specific programmed times
b. An occupant sensor that shall turn lighting off within for example 30 minutes of an occupant leaving a space, or
c. A signal from another control or alarm system that indicates the area is unoccupied (Energy Standard for Buildings Except Low-Rise Residential Buildings, 2010)
2.4.2 Space control
Each space enclosed by ceiling-height partition may have at least one control device to independently control the general lighting within the space. Each manual device is accessible by the occupants in order to control the lighting. (Energy Standard for Buildings Except Low- Rise Residential Buildings, 2010)
2.5 Service water heating
2.5.1 Electric water heater
Electric water heater is the simplest domestic hot water system requiring the minimum investment. However, in cool climates, domestic electric water heaters loads can contribute as much as 30% of the total household load. (Paull, Li, & Chang, 2010)
2.5.2 Thermosyphon system
The thermosyphon system is a simple and efficient system for domestic hot water supply.
However, its use is limited to warm regions where there is no frost danger. Due to the fact that the hot water tank is on the building’s roof, the aesthetic aspect should be taken into account.
2.5.3 Forced circulation system
This system is more advanced compared to the thermosyphon system. The hot water tank is in the internal and is connected both to a boiler and the solar collector. A controller
undertakes the task of mixing the water and providing the right hot water temperature.
2.5.4 Combi system
With a combi system, nearly zero energy buildings can be achieved. This system supplies solar domestic hot water and space heating. From a carbon efficiency perspective, the combi system is the optimal system for newly built or retrofitted buildings. (Colclough & McGrath, 2015)
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3 Multi-criteria decision analysis 3.1 The complexity of decisions
The complexity included in each decision problem is linked to three fundamental
parameters: a) the uncertainty parameter, b) the existence of multiple criteria and c) the preferences of the decision-maker. An additional, particularly critical parameter is the existence of multiple stakeholders. This parameter significantly contributes in increasing the complexity of each decision because of the interactions which stakeholders create with each other concerning goals and objectives.
The decision process is the result of the convergence of a programmed sequence of actions.
During this process, various events are taking place, such as gathering of information related to the problem of the decision, the exchange of views between stakeholders, conflict of interests or even fragmentation of the problem in individual problems and the partial solution of each one of them at different moments (Siskos & Hubert, 1983).
The stakeholder or actor is defined as the person or collective body who, either indirectly or directly, influences the decision process through the preferences system she/he adopts. The impact of the stakeholder involved in the decision process may be, either of first degree, as a result of her/his actions, or of second degree, as a result of the pressure she/he may exert on others.
The following are the actors involved in a decision process: a) the decision-maker, b) the analyst or facilitator, c) the client and (d) the third parties. Figure 3-1 illustrates how the stakeholders interact in a decision-making process. (Doukas & Psarras, 2014)
3.1.1 The characteristics of the decision-maker
The decision-maker of a problem is defined as that involved person whose objectives, constraints and preference system directly determine the development and final outcome of the decision-making process.
Figure 3-1 Stakeholders interaction in a decision-making process
Client
Decision Decision-maker
Support
Analyst Third parties
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The decision-maker in a decision process can be either a person, such as the chief executive officer of a company, the general secretary of a ministry, an official agent, etc., or a
collective body, such as a board of directors, a government committee, etc.
In most cases, the decision-maker constitutes an even more fuzzy entity or carrier. But even when she/he has been determined, she/he will likely express confusing and conflicting preferences. This fact constitutes a difficulty which should be successfully addressed during the decision support process. (Doukas & Psarras, 2014)
3.1.2 The role of the analyst
In general, the role of the analyst is to provide support in decision-making without substituting the role of the decision-maker. For this reason, the activity of an analyst is referred to as decision aiding. Decision aiding is someone’s activity who, using models, more or less formatted, contributes to the export of replies to questions asked by a stakeholder, especially a decision-maker, in a decision process. These questions are related with the quality of the decision as well as with the proof of its superiority over other decisions.
The role of the analyst in a decision process may be undertaken by a business researcher, a business consultant, a financial consultant, a system engineer etc. An analyst can either work individually, or lead a group. The contact she/he has with the decision-maker can be either a very close contact, as a result of a very frequent collaboration, or a first-time contact, in cases where the analyst collaborates with the decision-maker for the first time. (Doukas &
Psarras, 2014)
The role of the analyst should be the role of a person closely related with the decision- making process. On this basis, the analyst is addressed to both help the decision-maker to define the data and the decision variables and guide her/him throughout the decision- making process. However, in any case, the analyst’s position should be independent of the preference system she/he adopts. (Doukas & Psarras, 2014)
3.1.3 The client
Between the decision-maker and the analyst, the client acts as an authorized consultant of the decision-maker, contributing to the efficient communication between the two parties.
As in several cases the decision-maker does not come in direct contact with the analyst, the client will undertake the task of demonstrating the characteristics of the problem.
Additionally, she/he will take care in order to obtain all necessary data and information required and will oversee support process, on behalf of the decision-maker.
The client's role is particularly critical as, either in cases where the preferences of the decision-maker are not sufficiently specific, or in cases where the data required as input to the decision process is incomplete or unclear, she/he should collaborate with the analyst to overcome every difficulty. (Doukas & Psarras, 2014)
3.1.4 Third parties
Third parties in a decision process refer to those involved bodies who do not actively participate in it, but their preference system should be taken into account to some extent.
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The reason is that third parties are indirectly or directly affected by the consequences which result from the final decision. (Doukas & Psarras, 2014)
3.2 Objectives of multi-criteria decision analysis
Multi-criteria decision analysis is a sophisticated field of business research which over the past three decades has become extensively known both theoretically and practically. The simple finding that the solution of complex and essential decision-making problems is not possible through a one-sided and one-dimensional analysis played a key role for the development and spreading of the method.
Nonetheless, when examining all the parameters of a problem and the criteria/factors that influence the decision-making, a very important issue arises. The issue relates to the way in which all the parameters are synthesized to achieve rational decision-making. Sometimes, this issue can discourage decision-makers and analysts from adopting a more realistic approach.
Addressing this issue is the main objective of multi-criteria decision-making. But the main distinctive difference of multi-criteria analysis from other alternative approaches is not the simple synthesis of all the parameters of a problem. This is done through other
methodological approaches. The key feature of multi-criteria analysis is to make the
necessary synthesis in the light of decision-making policy and the system of preferences and values, which consciously or unconsciously is used by the decision-maker.
This feature is of particular importance in the field of decision-making. Obviously, the decision-maker is the final receiver of the result of any analysis carried out for the purpose of addressing a decision-making problem. Therefore, the development of decision-making models through methodological approaches that are unable to integrate the decision-maker and its preferences in the model development process attribute a passive role to the
decision-maker. This role is limited to monitoring and applying the results of mathematical models.
In the light of these observations, multi-criteria analysis has given special consideration in research related to the analysis, mathematical modeling and representation of preferences for decision-making policy on decision-maker’s side. The ultimate goal is to provide the necessary information to support the decision-making process while identifying the key features of the problem addressed and the specificities of the available alternatives. (Doukas
& Psarras, 2014)
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4 Basic concepts and methodology
The main subject of multi-criteria decision-making and a common element of all methodological approaches in this field is the development and the use of synthesis patterns. The basic parameters of the problem are included in the synthesis patterns in order to support the decision-maker in making rational decisions on the basis of her/his system of values and preferences. The goal completion is obviously a complex process which does not lead to optimal solutions and decisions, but to satisfactory solutions which respond to the general policy of the decision-maker.
A general methodological framework for dealing with multidimensional decision-making problems is presented below. This framework (Figure 4-1) essentially constitutes the backbone of every multi-criteria approach and it fully characterizes the philosophy of all the methodologies in this field. (Doukas & Psarras, 2014)
Figure 4-1 Framework of multi-criteria approach
As it can be seen in Figure 4-1, the process of analyzing the decision-making problems within the multi-criteria approach includes four stages. Between them, reactions may be
developed.
4.1 Multi-criteria decision analysis (MCDA) problem formulation
Generally, the MCDA problem for sustainable energy building decision-making involves m alternatives evaluated on n criteria. The grouped decision matrix can be expressed as follows:
criteria weights
alternatives - - -
X =
Where xij is the performance of j-th criteria of i-th alternative, wj is the weight of criteria j, n is the number of criteria and m is the number of alternatives. (Wang, Jing, Zhang, & Zhao, 2009)
Stage I
•Objective of decision- making
Stage II
•Consistent family of criteria
Stage III
•Preference model
Stage IV
•Support of decision- making
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5 Process and results 5.1 Case study
5.1.1 Step 1: Definition of the decision opportunity
The goal is to perform an energy pre-design for a new single-family dwelling in Athens, Greece. The building will have a total floor area of 120 m2 with a 40-year life expectancy. The preferred option for each subcategory of building component will be chosen among the possible options discussed in Chapter 2 Energy building pre-design options review. The subcategories of the building components are the sub-goals and the options are the decision alternatives.
5.1.2 Step 2: Identify Stakeholder preferences
For the purposes of the case study, a young couple interested in building their own home participated in the problem formulation by setting their own preferences and acting as the decision-makers.
Their preferences serve as the criteria by which to evaluate each building component.
Preferences were identified through a discussion with the decision-makers. The question imposed to reveal the key preferences for each alternative was:
- Among the roof/windows/walls/heating system/energy source for heating/power/lighting/
service water heating alternatives, which are the criteria that you would set to decide on the best for each one?
The homeowners of the new dwelling identified key preferences, many of which were further broken down into sub-preferences (Figures 5-1 to 5-8). Therefore, the problem has been specified as sub-goals, preferences (and sub-preferences) and alternatives.
5.1.2.1 Energy efficiency
For the energy design, achieving low energy consumption is the key issue. Cutting the energy usage in buildings can be achieved through scaling up the use of advanced construction and design techniques, high-performance insulation materials and intelligent controllers while promoting the use of renewable energy sources for heating, cooling and power.
5.1.2.2 Economic interest
Economic cost comprise of all costs relating to investment, operation and maintenance of:
construction materials, mechanical equipment, labor cost, installations, engineering services and other construction work. From the weight assigned to the economic interest, it can be concluded that it is essential and the most used criterion to evaluate energy systems. The stakeholders must consider the value of each cost when defining the preferences. For instance, envelope building components are characterized by high investment costs and low operating costs while energy for heating system and power generation are characterized by lower capital costs and higher operating costs. Therefore, not all kind of costs are taken into account in each decision framework.
5.1.2.3 Safety
The most common natural hazard in Greece is an earthquake. The high seismic activity of the Greek territory has led to reconsideration of the Greek Seismic Design Code and
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constant quality improvement of existing urban building envelopes. The seismic capacity of the structures is of great interest for the stakeholders and thus, the safety criterion is
considered for the selection of roof type. The safety criterion incorporates the basic safety of workers on the site of project as well.
5.1.2.4 Reliability
Reliability may be defined to the capacity of a building component to perform as designed.
The quality of the envelope building components, their maintenance and the energy savings offered play a great role in its reliability. Technical maturity is another criterion to evaluate the applied technology. Since maturity assures reliability, the maturity criterion is included in the reliability one. Measuring the degree of maturity of the technology can refer how
widespread the technology is at both national and international level. In detail, the following stages can be considered: technologies that are only performed in a very small percentage of new building constructions, technologies that could be still improved and consolidated technologies, which are close to reaching the theoretical limits of efficiency. Maturity is closely related to expertise of workers participating in a project.
5.1.2.5 Aesthetics
According to the ancient Roman architect Vitruvius, buildings should provide Commodity, Firmness and Delight. Commodity addresses the spatial and functional utility of a building.
Firmness addresses the building's ability to resist natural forces, starting with gravity. Delight relates to the sensory and associative pleasures buildings can provide. The designer must make design decisions that integrate aesthetics. Therefore, energy related building components must follow the above principle.
5.1.2.6 Comfort
People spend more than 90% of their life indoor. One of the main factors affecting indoor air quality is the heating system which should ensure thermal comfort (temperature and
humidity conditions that are comfortable for most occupants). Not all heating systems provide the same thermal comfort. In general, water supply heating systems are usually preferred by occupants against air supply heating systems. Apart from thermal comfort, space comfort is another comfort indicator for occupants. For instance, at the design phase, the extra space required for radiators and ducts has to be taken into consideration.
5.1.2.7 Independency
Independency interest may refer to the electric grid, fuel price fluctuations or utility fixed charges. Due to the rising energy costs, possible independency to some extent affects the final decision for power source and fuel for heating system. Especially, fuel costs may vary considerably in different time periods and areas as a result of several reasons including demand, production and policy matters.
5.1.3 Step 3: Build the decision frameworks
Based on the preferences discussed above, decision frameworks for each subcategory of building component were built (Figures 5-1 to 5-8) illustrating their relationship between the sub-goals as linkages.
15 Roof
Energy efficiency
Cost
Safety
Reliability
Investment
Maintenance
Flat roof, conventional, non-ventilated,
trafficable
Flat roof, ventilated,
trafficable
Flat roof with insulation, conventional, non-trafficable
Windows
Energy efficiency
Cost
Figure 1Decision framework for
windows selection
Aesthetics
Reliability
Investment
Maintenance
Aluminium windows with thermal bridge breaking system
PVC windows with thermal bridge breakage
Wood windows
Figure 5-2 Decision framework for windows selection Figure 5-1 Decision framework for roof selection
16 Walls
Energy efficiency
Investment cost
Aesthetics
Reliability
Brick cavity walls, with outer wall of facing bricks, 5
cm thick insulation
Brick cavity walls, with coated outer
wall of brickwork, 5 cm
thick insulation
Back-ventilated façade of brickwork, 5 cm
thick insulation Brick cavity
walls, with coated outer
wall of brickwork, 10
cm thick insulation
Curtain wall
Figure 5-3 Decision framework for walls selection
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Figure 5-4 Decision framework for heating system selection
Passive heating Heating
system
Energy efficiency
Cost
Aesthetics
Comfort
Investment
Maintenance
Radiator heating
Underfloor/wall/
roof heating
Electric underfloor/wall
/roof heating
Fireplace insert Thermal comfort
Space comfort
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Oil
Natural gas
Wood and pellet
Electrical energy
Heat pump Energy
source
Independency
Comfort
Cost Operation
Maintenance Investment Independen
cy from price fluctuations Independen
cy from fixed charges
Power
Cost
Grid independency
Operation
Maintenance
Grid fed
Solar electric or PV system Investment
Figure 5-5 Decision framework for selecting the energy source of the heating system
Figure 5-6 Decision framework for power source selection
19 Lighting
Cost
Operation
Space control
Automatic lighting shutoff Investment
Comfort
Service water heating
Cost
Operation
Electric water heater Investment
Comfort
Thermosyph on system
Forced circulation
system
Combi system Aesthetics
Figure 5-7 Decision framework for lighting selection
Figure 5-8 Decision framework for service water heating selection
20 5.1.4 Step 4: Rate the alternatives
Once key preferences that would be considered were identified, the task of rating the alternatives relative to how well they satisfied each preference was examined. An energy designer undertook the role of the consultant providing technical information which were necessary in order for the decision-makers to configure their preference system.
For example, questions like:
- Would a heavy roof affect the seismic capacity of the building?
- Which HVAC system is the most efficient?
- Which kind of water heater is most efficient for a three-member family?
were imposed by the decision-makers to the energy designer. Taking the advices of the designer into account, the decision-makers rated each alternative relative to the others.
Each alternative was rated relative to the others in satisfying a particular interest. A scale of 1-4 was used to assign points depending on which alternative satisfies the interest: the best
= 4; second best = 3; third best = 2; and the worst at satisfying the interest = 1.
For the sake of consistency, the steps of the MCDA method are presented only for the sub- goal Roof. In the end of the chapter, aggregated data for all the sub-categories are available in tables (5-3 to 5-10).
Table 5-1 Rate of interests/alternatives
Interest Flat roof,
conventional, non- ventilated, trafficable
Flat roof, ventilated, trafficable
Flat roof with insulation, conventional, non-
trafficable Heating and cooling
efficiency
1 3 4
Investment cost 1 2 4
Maintenance cost 2 2 4
Reliability 1 2 2
In order to serve as an accurate consultant, the energy designer often had to consult several sources. When it comes to heating and cooling efficiency, the U value of construction types is an essential parameter. For the purpose of efficiency calculation, the designer used a quick tool to calculate the U value of the construction types. The software program used is TiSoft U Value calculator and it enables the calculation of U value and the 3D visualization for various construction types.
Data for investment and maintenance costs for the construction types were retrieved from the article of (Huedo, Mulet, & Lopez-Mesa, 2016).
5.1.5 Step 5: Weight Stakeholder interests
All factors have their internal impact reclassified to a common scale so that it is necessary to determine each interest’s relative impact in the MCDA problem (Wang, Jing, Zhang, & Zhao,
21
2009). Weights were assigned by allocating 100 points among the interests and sub- interests.
Table 5-2 Weight of stakeholder interests and sub-interests
Interest Weight Sub-interest Weight
Heating and cooling efficiency
60 Heating and cooling efficiency 60
Cost 30 Investment 20
Maintenance 10
Reliability 10 Reliability 10
According to table 5-2, among the interests concerning the stakeholders, heating and cooling efficiency is of highest concern, followed by investment cost. Maintenance cost and reliability are of equal, low importance.
5.1.6 Step 6: Score the alternatives
The preferred option for the building component is identified by multiplying the sub-interest weight by its corresponding rating value to calculate a score for that sub-interest. Summing the score, it yields the most preferred option.
Table 5-3 Scoring of roof alternatives
Sub-interest Weight Rating Score
Flat roof, conventional, non- ventilated, trafficable (R1)
Flat roof, ventilated, trafficable (R2)
Flat roof with insulation, conventional, non-
trafficable (R3)
R1 R2 R3
Heating and cooling efficiency
60 1 3 4 60 180 240
Investment
cost 20 1 2 4 20 40 80
Maintenance
cost 10 2 2 4 20 20 40
Reliability 10 1 2 2 10 20 20
Totals 110 260 380
A seen in table 5-3, flat roof with insulation, conventional, non-trafficable is the dominant choice, gaining the highest score for all sub-interests.
22
Table 5-4 Scoring of windows alternatives
Sub- interest
Weight Rating Score
Aluminium windows with thermal bridge breaking system (W1)
PVC windows with thermal bridge breakage (W2)
Wood windows
(W3)
W1 W2 W3
Energy
efficiency 10 4 4 1 40 40 10
Investment
cost 60 3 4 2 180 240 120
Maintenance
cost 5 4 4 1 20 20 5
Reliability 5 4 4 1 20 20 5
Aesthetics 20 2 1 4 40 20 80
Totals 300 340 220
PVC windows with thermal bridge breakage are preferred among the alternatives mainly thanks to their low investment cost (table 5-4).
Table 5-5 Scoring of walls alternatives
Sub- interest
Weight Rating Score
BW1 BW2 BW3 BW4 Curtain wall
BW1 BW2 BW3 BW4 Curtain wall Energy
efficiency 40 3 3 3 4 1 120 120 120 160 40
Investment
cost 30 4 4 4 3 1 120 120 120 90 30
Aesthetics 20 2 4 4 1 3 40 80 80 20 60
Reliability 10 3 4 4 2 1 30 40 40 20 10
Totals 310 360 360 290 140
According to table 5-5, BW2 and BW3 have equal score which means that brick cavity walls, with coated outer wall of brickwork, either 5 cm or 10 cm thick are preferred for the construction.
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Table 5-6 Scoring of heating system alternatives
Sub- interest
Weight Rating Score
Radiator heating (H1)
UFH (H2)
Electric UFH (H3)
Fireplace insert (H4)
Passive heating (H5)
H1 H2 H3 H4 H5
Energy
efficiency 60 2 3 3 1 4 120 180 180 60 240
Investment
cost 10 4 2 3 4 1 40 20 30 40 10
Maintenance
cost 5 2 2 3 3 2 10 10 15 15 10
Aesthetics 10 1 4 4 2 2 10 40 40 20 20
Thermal
comfort 10 3 4 4 2 2 30 40 40 20 20
Space
comfort 5 1 4 4 3 2 5 20 20 15 10
Totals 215 310 325 170 310
In table 5-6, it can be observed that electric underfloor heating is the most preferred option, closely followed by water underfloor heating and passive heating.
Table 5-7 Scoring of energy source for heating system alternatives
Sub-interest Weight Rating Score
Oil (F1)
Natural gas (F2)
Wood and pellet
(F3)
Electric energy (F4)
Heat pump (F5)
F1 F2 F3 F4 F5
Independency from fixed charges
20 1 1 4 1 2 20 20 80 20 40
Independency from price fluctuations
10 1 1 3 1 2 10 10 30 10 20
Investment
cost 10 4 3 4 3 1 40 30 40 30 10
Operation cost 50 1 3 2 4 4 50 150 100 200 200
Maintenance
cost 5 1 2 2 4 3 5 10 10 20 15
Comfort 5 3 4 1 1 3 15 20 5 5 15
Totals 140 240 265 285 300
Table 5-7 demonstrates the scoring of solutions where heat pump is the dominant one.
24
Table 5-8 Scoring of power source alternatives
Sub-interest Weight Rating Score
Grid fed Solar electric or PV system Grid fed Solar electric or PV system
Investment cost 50 4 1 200 50
Operation cost 20 1 4 20 80
Maintenance cost 20 4 1 80 20
Grid independency 10 1 4 10 40
Totals 310 190
According to the stakeholders scoring, a grid fed house is clearly preferred over one that is fed by solar electric or PV system (table 5-8).
Table 5-9 Scoring of lighting alternatives
Sub-interest Weight Rating Score
Space control
Automatic lighting shutoff
Space control
Automatic lighting shutoff Investment
cost 30 2 3 60 90
Operation cost 10 2 4 20 40
Comfort 60 4 2 240 120
Totals 320 250
As it can be seen by table 5-9, stakeholders would choose space control rather than automatic lighting shutoff.
Table 5-10 Scoring of service water heating alternatives
Sub- interest
Weight Rating Score
Electric water heater (S1)
Thermosyphon system (S2)
Forced circulation system (S3)
Combi system (S4)
S1 S2 S3 S4
Investment
cost 20 4 3 2 1 80 60 40 20
Operation
cost 40 1 2 3 4 40 80 120 160
Comfort 30 1 2 3 4 30 60 90 120
Aesthetics 10 4 1 2 2 40 10 20 20
Totals 190 210 270 320
A combi system would best cover the needs of the stakeholders, according to table 5-10.
25
6 Discussion
Following the MCDA method, a combination of building components has been configured.
However, several results have to be questioned for their validity. Equal scoring of walls alternatives has raised an issue related to the low accuracy of rating method. The walls differ on their insulation thickness but this fact has not been imprinted on the results. In addition, electric underfloor heating system has been rated as the most favorable although it cannot be combined with an air-to-water heat pump. A last significant notice is that space control and automatic lighting shutoff are not necessarily alternatives. A combination of the above could be found in a building.
Multiple MCDA methods have been developed and proposed for the pre-design of energy systems. The most relevant of them are mentioned in the literature review. Within the scope of the thesis, the simplest MCDA method was applied generating results that differ from results available in the literature. The main reason is that less amount of variables were used in the simplified method and thus, the various results cannot be directly compared.
7 Conclusions
The multi-criteria decision analysis method proposed in this thesis can be used to locate optimum or near optimum green building designs for given conditions. Criteria weights directly influence the decision-making results of energy design alternatives. It can be observed that energy efficiency, investment cost and maintenance cost are the most common criteria.
The goal of filling the literature gap of a simplified method for holistic energy pre-design has been achieved to a satisfying extent. Results yield that the method is suitable for a basic energy ‘draft’ but would not be proven suitable when an energy pre-study must be performed.
In the context of this thesis, building components have been treated individually. This approach has been followed because the initial goal was to demonstrate an easy-to-use method which would facilitate the designer. Subsequently, it was proved that combinations of building components should be investigated in order to generate more accurate results with applicability. The approach where the five technical distinct components of the building create multiple combinations of design scenarios could be the basis for future research.
Besides, more complex and precise methods could be followed like the ones mentioned in literature review.
As long as criteria selection and weights, MCDA methods and aggregation methods are appropriate and suitable to the specific decision problems, multi-criteria decisions analysis can become a powerful tool in the pursuit of a sustainable society.
26
8 Bibliography
Colclough, S., & McGrath, T. (2015). Net energy analysis of a solar combi system with Seasonal Thermal Energy Store. Applied Energy , 611-616.
Doukas, C., & Psarras, I. (2014). Models of policy decisions in energy and environmental systems. Athens: Symmetria.
Echenagucia, T. M., Capozzoli, A., Cascone, Y., & Sassone, M. (2015). The early design stage of a building envelope: Multi opjective search through heating, cooling and lighting energy performance analysis. Applied Energy , 577-591.
Energy Standard for Buildings Except Low-Rise Residential Buildings. (2010). Atlanta:
ANSI/ASHRAE/IES Standard 90.1-2010.
Huedo, P., Mulet, E., & Lopez-Mesa, B. (2016). A model for the sustainable selection of building envelope assemblies. Environmental Impact Assessment Review , 63-77.
Pacheco, R., Ordonez, J., & Martinez, G. (2012). Energy efficient design of building: A review.
Renewable and Sustainable Energy Reviews , 3559-3573.
Papadopoulos, A. M., Oxizidis, S., & Papandritsas, G. (2008). Energy, economic and environmental performance of heating systems in Greek buildings. Energy and Buildings , 224-230.
Paull, L., Li, H., & Chang, L. (2010). A novel domestic electric water heater model for a multi- objective demand side management program. Electric Power Systems Research , 1446-1451.
Siskos, J., & Hubert, P. (1983). Multi-criteria analysis of the impacts of energy alternatives: A survey and a new comparative approach. European Journal of Operational Research , 278- 299.
Wang, J.-J., Jing, Y.-Y., Zhang, C.-F., & Zhao, J. H. (2009). Review on multi-criteria decision analysis aid in sustainable energy decision-making. Renewable and Sustainable Energy Reviews , 2263-2278.
Wang, W., Zmeureanu, R., & Rivard, H. (2005). Applying multi-objective genetic algorithms in green building design optimization. Building and Environment , 1512-1525.
